The .300 Weatherby is substantially more gun than the 7mm Rem Mag. I have both, and like both. But if I were hunting Bears, something that if it got mad at me and decided, unlike other animals that almost always run away, to kill me, I'd have to stop it with my gun, I'd go with a .340 Weatherby Magnum. The .30-378 is one cannon too.

The .338 Winchester Mag, as is mentioned above, is a thumper too, but won't gain you enough over the .300 Weatherby to bother.

I wouldn't go with a 7mm Remington Mag for big bears.